unpartioning sd card

Hi, my mate decided to partition his sd card on his rooted hero , now it is only saying 5gb instead of 8gb, and he wants to take the partition off but for some reason he cant. He did say that the card isnt being reconised by his computer too , and he thinks he has lost all of his data too (Unless it is in the other 2gb) what is the best way if any to revert back to a unpartitioned sd card?